3,3'-Diaminobenzidine (DAB) (CAS No. 91‑95‑2; Chemical Formula: C₁₂H₁₄N₄) is a white to beige crystalline powder commonly used as a chromogenic substrate in immunohistochemistry (IHC) and blotting techniques. Upon oxidation, DAB forms an insoluble brown product, enabling precise visualization of antigen-antibody binding in diagnostic and research applications.